Anisotropy of radiation-induced degradation in mechanical properties of fabric-reinforced polymer-matrix composites

Four kinds of fabric-reinforced polymer-matrix composites (filler: E-glass or carbon fabric; matrix: epoxy or polyimide resin) were irradiated with 60Co γ-rays or 2 MeV electrons at room temperature. Three-point bend tests were then carried out at 77 K and at room temperature in a 450 direction from warp to fill. Comparison of the degradation behaviour reveals that the glass-epoxy and glass-polyimide composites are quite similar to each other in the dose dependence of the ultimate interlaminar shear strength at each test temperature. This suggests that the radiation damage at the fibre-matrix interface decreases the contribution of the chemical bond mode to the total bond strength at the interface, thus decreasing the composite shear strength with increasing dose. For the carbon-epoxy and carbon-polyimide composites, however, the shear strength at room temperature changes little even after irradiation up to 140 MGy, while the shear strength at 77 K decreases monotonically with increasing dose. This suggests that the fibre-matrix bond strength due to the friction force mode is quite insensitive to radiation, thus resulting in the dose-independent shear strength at room temperature. At 77 K, however, the friction force mode fails to function properly because of the brittleness of the matrix resin, and consequently the composite shear strength decreases with increasing dose owing to a resulting increase in the matrix brittleness. (author)